Post-irradiation identification of papaya (Carica papaya L.) fruit

Impact of radiation processing on the volatile essential oil profile of papaya (Carica papaya) was investigated. Gamma-radiation processing resulted in the appearance of a new peak in the GLC profile that was identified as phenol. The observed dose dependent increase in phenol content suggested possible use of this compound as a marker for radiation processed papaya.     

Conformational polymorphism in bicalutamide: a quantum chemical study

Bicalutamide is an anti-neoplastic drug widely used for the treatment of prostate cancer and it exhibits conformational polymorphism. Three crystal structures of bicalutamide are reported as racemic mixtures, two of which are polymorphs. In addition, three co-crystals are also reported—two with organic coformers and one with adrenoreceptor (the macromolecular target). All the reported structures show significant conformational differences. Quantum chemical B3LYP/6-31+G(d,p) analysis has been carried out to understand the interplay of intra- and intermolecular interactions leading to the conformational preferences in this molecule. The difference between the two polymorphic forms has been traced to the C5–S8–C11–C12 torsional angle. Inside the cavity of androgen receptor, a completely different conformation is found but it does not correspond to any local minima on the potential energy surface of the drug. A relatively rigid torsional angle C11–C12–C15–N17 is also expected due to a strong five-membered ring intramolecular hydrogen bond (H–O13–C12–C15–O16), which has been reported to be desirable; quantum chemical analysis revealed that this rigidity is of the order of 11 kcal/mol. Ab initio calculations demonstrate that polymorphs and polymorphic co-crystals differ in the extent of intra- and intermolecular hydrogen bonding interactions. The strength of the intermolecular interactions associated with these structures is analyzed in terms of energy release due to dimerization.     

Influence of water on anharmonicity, stability, and vibrational energy distribution of hydrogen-bonded adducts in atmospheric reactions: case study of the OH + isoprene reaction intermediate using ab initio molecular dynamics

The effect of water on the stability and vibrational states of a hydroxy-isoprene adduct is probed through the introduction of 1-15 water molecules. It is found that when a static nuclear harmonic approximation is invoked there is a substantial red-shift of the alcohol O-H stretch (of the order of 800 cm(-1)) as a result of introduction of water. When potential energy surface sampling and associated anharmonicities are introduced through finite temperature ab initio dynamics, this hydroxy-isoprene OH stretch strongly couples with all the water vibrational modes as well as the hydroxy-isoprene OH bend modes. A new computational technique is introduced to probe the coupling between these modes. The method involves a two-dimensional, time-frequency analysis of the finite temperature vibrational properties. Such an analysis not only provides information about the modes that are coupled as a result of finite-temperature analysis, but also the temporal evolution of such coupling.     

Chiroptical spectroscopy of surfactants

Three different chiroptical spectroscopic methods, namely, optical rotation, electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) have been evaluated for studying the aggregation of sodium dodecylsulfate (SDS), an achiral surfactant, using garcinia acid disodium salt (GADNa) as a chiral probe. The specific rotation and ECD of GADNa are found to be altered by the aggregation of SDS, suggesting for the first time that achiral surfactants can be characterized with chiroptical spectroscopy using appropriate chiral probes. In addition, a chiral compound, fluorenyl methyloxy carbonyl l-leucine sodium salt (FLNa) is found for the first time to behave as a surfactant in water, with 205 ?(2) surface area per molecule at the air-water interface, critical micelle concentration (CMC) of 0.18 M, and Gibbs energy of micellization of -14 kJ/mol. The specific rotation of FLNa in water is found to increase with concentration beyond CMC, suggesting the formation of chiral aggregates. Different conformations of FLNa amenable to micellization have been identified using quantum chemical conformational analysis and their specific rotations calculated. The formation of lamellar aggregates of FLNa in water is suggested to be the cause for increase in specific rotation with concentration beyond CMC.     

Remarkable photocytotoxicity of curcumin in HeLa cells in visible light and arresting its degradation on oxovanadium(IV) complex formation

Curcumin (Hcur) as a cellular imaging and PDT agent shows remarkable photocytotoxicity in HeLa cells in visible light of 400-700 nm giving IC(50) = 8.2 ± 0.2 μM and its degradation is arrested on formation of photocytotoxic dipyridophenazine (dppz) complex [VO(cur)(dppz)Cl] (IC(50) = 3.3 ± 0.4 μM), while both are less toxic in the dark.     

A new approach to construct a fused 2-ylidene chromene ring: highly regioselective synthesis of novel chromeno quinoxalines

Regioselective construction of a fused 2-ylidene chromene ring was achieved for the first time by using AlCl(3)-induced C-C bond formation followed by Pd/C-Cu mediate coupling-cyclization strategy. A number of chromeno[4,3-b]quinoxaline derivatives were prepared by using this strategy. Single crystal X-ray diffraction study of a representative compound e.g. 6-(2,2-dimethylpropylidene)-4-methyl-6H-chromeno[4,3-b]quinoxalin-3-ol confirmed the presence of an exocyclic C-C double bond with Z-geometry. The crystal structure analysis and hydrogen bonding patterns of the same compound along with its structure elaboration via propargylation followed by Sonogashira coupling of the resulting terminal alkyne is presented. A probable mechanism for the formation of 2-ylidene chromene ring is discussed. Some of the compounds synthesized showed anticancer properties when tested in vitro.     

Selective oxidation of organic sulfides by mononuclear and dinuclear peroxotungsten(VI) complexes

Clean conversion of a variety of sulfides and dibenzothiophene (DBT) to the corresponding sulfoxide or sulfone could be achieved in high yields at room temperature using mononuclear as well as dinuclear diperoxo complexes of tungsten as oxidants, by a variation of reaction conditions. The compounds could also effectively catalyze oxidation of sulfides by H₂O₂ to selectively yield sulfone with reasonably good turnover frequency (TOF).     

A novel one-pot synthesis of spiro[indoline-3,4′-pyrazolo[3,4-e][1,4]thiazepine] diones using recyclable bioglycerol-based sulfonic acid functionalized carbon catalyst

A novel, simple, and efficient synthetic protocol has been developed for the synthesis of spiro[indoline-3,4′-pyrazolo[3,4-e][1,4]thiazepine] diones, by using bioglycerol-based sulfonic acid functionalized carbon as a recyclable catalyst, devoid of moisture sensitive metal catalysts and corrosive acidic reagents. This new protocol produces novel heptacyclic spirooxindole derivatives in good to excellent yields, with operational simplicity and recycling of the catalyst in comparison to predictable pentacyclic compounds. The catalyst can be prepared by a simple adoptable procedure from an inexpensive and readily available bio-glycerol and found to be recoverable and reusable up to four cycles without any loss of activity.     

Microwave assisted synthesis of indolo[2,3-b]dibenzo[b,g][1,8]naphthyridines

We have developed an effective microwave assisted p-TsOH catalyzed synthesis of indolo[2,3-b]dibenzo[b,g][1,8]naphthyridines via a one pot reaction of 3-amino-9-ethylcarbazole and 2-chloro-3-formylquinolines.     

Building-up Remarkably Stable Magnesium Porphyrin Polymers Self-Assembled via Bidentate Axial Ligands: Synthesis, Structure, Surface Morphology, and Effect of Bridging Ligands

A series of supramolecular architectures of magnesium tetranitrooctaethylporphyrins mediated by several bidentate axial ligands have been synthesized in excellent yields and structurally characterized. Six conjugated axial ligand with increasing chain lengths have been utilized in the present investigations in which the Mg···Mg nonbonding distance between successive ions also increases from 0.73 to 2.70 nm in the series. To the best of our knowledge, this is the first report where stable metallo-porphyrin polymers with such long spacers have been synthesized in one pot so easily. Linear one-dimensional (1D) polymeric chains were observed in the X-ray structure of the six-coordinated complexes in which porphyrin units are aligned parallel to each other to have so-called "shish kebab" like architectures to maintain offset-stacked overlap. However, after an optimum Mg···Mg nonbonding distance, these 1D chain do not continue, rather they form five-coordinated porphyrin dimers with "wheel-and-axle" like architectures which are then self-aggregated by π-π interactions in a perpendicular manner to fill space created by large bridging ligands more effectively which consequently results in spherical structures. The structures of the molecules in solution and their surface patterns on highly ordered pyrolytic graphite (HOPG) have also been investigated.